U.S. Secretary of State Mike Pompeo on Friday lambasted his predecessor, John Kerry, for meeting Iranian officials in back-channel talks and accused him of trying to undermine the Trump administration's policy toward Tehran.

"What Secretary Kerry has done is unseemly and unprecedented," Pompeo told a news conference, adding that he "ought not to engage in that kind of behavior. It's inconsistent with what the foreign policy of the United States is, as directed by this president. It is beyond inappropriate."

Pompeo's crack at Kerry comes a day after President Donald Trump accused the former secretary of state of "illegal meetings with the very hostile Iranian Regime" in a late-night tweet.

Trump withdrew the United States from a nuclear deal with Iran that Kerry negotiated between Iran and six world powers in 2015. The Trump administration has pushed a hard line against Tehran as it moves to reimpose sanctions that were lifted against Iran since the deal.

Kerry, in a radio interview with Fox News as part of a book tour, said he had met with Iranian Foreign Minister Mohammad Javad Zarif "three or four times" since the end of his term in January 2017. He has also accused the Trump administration of pursuing a policy of regime change in Iran.

"This is a former secretary of state engaged with the world's largest state sponsor of terror and according to him ... he was talking to them," Pompeo said, adding: "He was telling them to wait out this administration. You can't find precedent for this in U.S. history."

Pompeo also denied that the administration was seeking so-called regime change in Iran.

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